I had written a non-prototype several years ago like this:
var _singletons = []; // for storing singleton instances of objects
Function.prototype.singleton = function (o) {
if(!_singletons[this.name]) {
_singletons[this.name] = o;
return false;
}
return true;
}
Function.prototype.getSingleton = function () {
return _singletons[this.name];
}
then you define a class like this:
function AClass() {
if AClass.singleton(this) return AClass.getSingleton();
this.a = a;
/* etc */
}
That way you can call var a = new AClass() as many times as you like
and it'd return the same object instance every time. Which I think is
close to a real singleton instance of an object.
But I don't think you could do that readily with Prototype using the
Class.create() mechanism.
On 22/05/06, Nicolas Terray <[EMAIL PROTECTED]> wrote:
On 5/22/06, Grzesiek Slusarek <[EMAIL PROTECTED]> wrote:
> Hello all. I'm writing my own object using prototype and I
> wonder how you write and call only one instance of class. Can
> anyone share his idea of singleton?
> thanks
> Gregor
>
Here is my proposal :
---8<----------------------
<script>
var Foo = Class.create();
Object.extend(Foo.prototype, {
initialize: function() {
this.a = 5;
}
});
Object.extend(Foo, {
instance: function() {
if (!this._instance) {
this._instance = new Foo();
}
return this._instance;
}
});
var o1 = Foo.instance();
var o2 = Foo.instance();
alert(o1.a + ' ' + o2.a);
o2.a = 10;
alert(o1.a + ' ' + o2.a);
</script>
---8<----------------------
Anyway it is not a real singleton since it is possible to call the
constructor outside from instance()
Furthermore, by hacking Foo, I do not know if I break something by
adding _instance and instance() :-\
Yours,
Nicolas Terray
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--
Andrew Tetlaw
htp://tetlaw.id.au
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